Method of removing residual peroxide catalyst from resin coatings



METHQD F REMOVHNG RESIDUAL PERCXIDE CATALYST FROM RESIN COATINGS Howard(C. Haas, Arlington, Mass., assignor to Polaroid Corporation, Cambridge,Mass, a corporation of Dela- Ware No Drawing. Application November 18,1957 Serial No. 696,899

13 Claims. (Cl. 11762) This invention relates to high polymers and moreparticularly to novel processes for treating plastic coatings, films andlaminates.

One object of this invention is to provide novel processes fordeactivating residual peroxide catalysts in plastic coatings, films andlaminates.

Another object of this invention is to provide processes wherein thisdeactivation may be carried out at low temperatures and without causingexcessive swelling or distortion of the materials.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the process involving the severalsteps and the relation and order of one or more of such steps withrespect to each of the others which are exemplified in the followingdetailed disclosure, and the scope of the application of which will beindicated in the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description.

It is often necessary and desirable to deactivate residual peroxidecatalysts in plastic coatings, films and laminates in order to preventharmful side reactions. Such catalysts may, for example, causeundesirable dye discoloration due to the oxidation of dyes which may beincorporated in the coatings or films themselves or in other layers of alaminate. When polymerization is effected prior to application andprocessed in solvents or in a thermoplastic state, no seriousdifficulties arise because the residual peroxide catalyst may be readilydeactivated prior to application by methods known to the art such as,for example, decomposition with organic primary and secondary amines,baking at high temperatures, solvent extraction, etc. However, whenpolymerization is effected in situ, the before mentioned deactivatingmethods often do not lend themselves to the task because of excessiveswelling, undesirable decomposition products, distortion, crazing, etc.

The present invention provides processes wherein residual peroxidecatalysts present in polymeric coatings, films and laminates may beeffectively decomposed without substantially altering, distorting, etc.the polymer. The processes comprise exposing said coatings, films andlaminates to the hydrogen iodide vapors of an aqueous hydrogen iodidesolution and, after exposure, driving ofi, at a relatively lowtemperature, the iodine which is produced as a result of thedecomposition.

The processes herein disclosed are especially useful on thermosettingcrosslinked polymeric surface coatings, which today are widely used asmar-resistant finishes for plastic sheets and laminates. Such polymers,because of their inherent insolubility and lack of thermoplasticity,must be polymerized subsequent to application and, thus, generallycontain residual peroxides which may, as previously noted, have harmfuleffects on the finished product.

The processes of this invention are particularly useful tates Patm indecomposing the residual peroxide catalysts in the mar-resistant surfacecoatings of the plastic optical elements disclosed in the copendingapplication of Elkan R. Blout, H. O. Buzzell and Leonard Farney, SerialNo. 539,219, filed October 7, 1955. Generally, the optical elementstherein disclosed comprise laminated sheets of thermoplastic polymerscoated on both surfaces with a crosslinked polymer of adiethylenic-substituted polyethyleneglycol monomer such, for example, astetraethyleneglycol dimethacrylate. In one of the specific embodimentsdisclosed therein, the optical element comprises a laminate of a centrallayer of light-polarizing material such, for example, as molecularlyoriented polyvinyl alcohol which has been dyed or stained with adichroic dye, usually a dye comprising iodine and an iodide. Thiscentrally disposed layer or film of polarizing material is bonded oneach of its surfaces to a sheet of a cellulosic compound such, forexample, as cellulose acetate butyrate or cellulose acetate. Thecellulosic layers in turn are coated with the mar-resistant surfacecoatings. The surface coating is preferably applied by coating thecellulosic surfaces with a thin layer of a diethylenicsubstitutedpolyethyleneglycol monomer containing a peroxide catalyst such, forexample, as diisopropyldipercarbonate, and polymerizing it in contactwith a heated, optically smooth surface. In certain instances such, forexample, as when the optical elements are to be used as sunglasses, thecellulosic layers may contain a dye or dyes. It has been found that ifthe residual peroxide catalyst is not deactivated, it will migrate intothe cellulosic layers during aging and oxidize the dyes containedtherein and result in discoloration. The processes disclosed hereinprovide means whereby deactivation may be carried out without alteringor distorting the optical elements.

In carrying out the processes herein disclosed, the coatings, films orlaminates to be deactivated are preferably disposed in a closed chambercontaining the hydrogen iodide vapors of an aqueous hydrogen iodidesolution. In a preferred mode of carrying out this invention, the sourceof hydrogen iodide vapors is about a 47% aqueous solution. However,higher or lower concentrations may be used. The processes may be carriedout at room temperature and preferably are carried out at a slightlyelevated temperature such, for example, as 45 C., but it is contemplatedthat higher temperatures may be used. The time of exposure will varydepending upon factors such as amount of residual catalyst present,permeability of the polymer to the hydriodic acid, thickness of thecoating, temperature, concentration of the hydriodic acid, etc. In mostcases, exposure for two hours at 45 C. will substantially destroy anyresidual peroxide catalyst. The iodine which is produced as a result ofthe decomposition may cause the polymers to turn slightly brown.However, baking at about 70 C. for about two hours will usually besufficient to drive off the residual iodine and restore the polymer toits original color.

The following nonlimiting example illustrates a process within the scopeof this invention:

Example 1 A laminate, comprising a center layer of a molecularlyorientated polyvinyl alcohol sandwiched between two sheets of celluloseacetate butyrate, is coated on both surfaces with a solution comprising:

Grams Tetraethyleneglycol dimethacrylate Cellulose nitrate (thickener)10 Diisopropyldipercarbonate 0.75

and heated in an air-free atmosphere between two optically smoothplatens for about three minutes at 80 to 100 C. to form a layerapproximately 0.001 inch thick.

The above laminated sheet is placed in an oven containing a beaker of47% aqueous hydrogen iodide for about two hours at 45 C. At the end ofthe two hour period, the sheet is baked at 70 C. for about another twohours to remove the residual iodine. An examination of the sheet showsno visual severance of the bonding or excessive distortion or swelling.Upon testing for residual diisopropyldipercarbonate with a solutioncomprising 2% benzidine in aqueous acetic acid, the results werenegative. An abrasion test indicated that the treatment had no effect onthe mar-resistance of the coating.

It should be noted that the processes herein disclosed are not limitedto deactivating dipercarbonate catalysts but, are elfective on peroxidecatalysts in general. As examples of additional peroxide catalysts whichmay be deactivated, mention may be made of peroxides of aromatic acids,such as benzoyl peroxide and substituted benzoyl peroxides; peroxides ofaliphatic acids such as lauroyl peroxide; ketone peroxides such asmethyl amyl ketone peroxide; aldehyde peroxides; dialkyl peroxides suchas di-t-butyl peroxide; hydroperoxides such as t-butyl hydroperoxide andperoxide esters such as t-butyl-perbenzoate.

As examples of other polymers which may be treated by the processesherein disclosed, mention may be made of dimethacrylates,polyalkylmethacrylates such as methylmethacrylate and ethylmethacrylate,polyacrylates, polyacrylic and polymethacrylic acid polymers,polyhydrocarbons such as polystyrene, poly alkyl vinyl ketones such asmethyl vinyl ketone and thermosetting polyesters.

When the processes of this invention are used on halogen-substitutedpolymers such, for example, as vinyl chloride and vinylidene chlorides,the hydrogen iodide vapors may accelerate the evolution of hydrogenchloride and suitable precautions such, for example, as low temperaturesand dilute solutions of the hydrogen iodide should be employed in orderto keep the hydrogen chloride evolution at a minimum.

Since certain changes may be made in the above process without departingfrom the scope of the invention herein involved, it is intended that allmatter contained in the above description shall be interpreted asillustrative and not in a limiting sense.

What is claimed is:

1. A process for decomposing residual peroxide catalysts in plasticcoatings, films and laminates, said process comprising exposing thepolymer to the hydrogen iodide vapor of an aqueous solution of hydrogeniodide.

2. A process as defined in claim 1 including the step of subsequentlybaking said polymer to drive ofi iodine which is produced as a result ofthe decomposition.

3. A process as defined in claim 1 wherein said hydrogen iodide vapor issupplied from about a 47% aqueous solution.

4. A process as defined in claim 1 wherein said exposure is carried outat about 45 C.

5. A process as defined in claim 2 wherein said baking is carried out atabout C.

6. A process as defined in claim 1 wherein said polymer is a crosslinkedpolymer.

7. A process for decomposing residual peroxide catalysts in adiethylenic-substituted polyethylencglycol polymeric surface coating,said process comprising exposing said coating to the hydrogen iodidevapor of an aqueous solution of hydrogen iodide.

8. A process as defined in claim 7 including the step of subsequentlybaking said coating to drive off iodine produced as a result of thedecomposition.

9. A process as defined in claim 7 wherein said hydrogen iodide vapor issupplied from about a 47% aqueous solution.

10. A process as defined in claim 7 wherein said exposure is carried outat 45 C.

11. A process as defined in claim 7 wherein said coating is a polymer oftetraethyleneglycol dimethacrylate.

12. A process for decomposing residual peroxide catalysts in crosslinkedpolymeric surface coatings on plastic, light-polarizing opticalelements, said process comprising exposing said element to the hydrogeniodide vapors of an aqueous hydrogen iodide solution.

13. A process as defined in claim 12 including the step of subsequentlybaking said element to drive off the iodine which is produced as aresult of the decomposition.

14. A process as defined in claim 12 wherein said hydrogen iodide vaporis supplied from about a 47% aqueous solution.

15. A process as defined in claim 12 wherein said exposure is carriedout at about 45 C.

16. A process as defined in claim 13 wherein said baking is carried outat about 70 C.

17. A process as defined in claim 12 wherein said crosslinked polymericsurface coating is a polymer of a diethylenic-substitutedpolyethyleneglycol.

18. A process as defined in claim 12 wherein said crosslinked polymericsurface coating is a polymer of tetraethyleneglycol dimethacrylate.

References Cited in the file of this patent UNITED STATES PATENTS2,104,760 Renfrew Jan. 11, 1938 2,143,941 Crawford Jan. 17, 19392,450,503 Drummond Oct. 5, 1948 2,628,178 Burnett Feb. 10, 1953

1. A PROCESS FOR DECOMPOSING RESIDUAL PEROXIDE CATELYSTS IN PLASTICCOATINGS, FILM AND LAMINATES, SAID PROCESS COMPRISING EXPOSING THEPOLYMER OF HYDROGEN IODIDE VAPOR OF AN AQUEOUS SOLUTION OF HYDROGENOIDIDE.